Understanding Common Salt (NaCl) Composition

Common salt, scientifically known as sodium chloride ($\text{NaCl}$), is a widely used substance in our daily lives, found in kitchens and also important in various industrial processes. Understanding its chemical composition involves looking at how it is formed.

Formation of Salts: Neutralization Reactions

Salts are typically formed through a chemical reaction between an acid and a base. This type of reaction is called a neutralization reaction. In a neutralization reaction, the acid and base react to produce a salt and water.

The general reaction is:

Acid + Base → Salt + Water

Parent Components of Common Salt (NaCl)

To determine what type of acid and base make up common salt ($\text{NaCl}$), we need to identify the specific acid and base that react to form it.

• The base that contains the sodium ion ($\text{Na}^+$) in $\text{NaCl}$ is sodium hydroxide ($\text{NaOH}$).
• The acid that contains the chloride ion ($\text{Cl}^-$) in $\text{NaCl}$ is hydrochloric acid ($\text{HCl}$).

The reaction forming $\text{NaCl}$ is:

$\text{HCl}\text{(aq)} + \text{NaOH}\text{(aq)} \rightarrow \text{NaCl}\text{(aq)} + \text{H}_2\text{O}\text{(l)}$

Strength of Parent Acid and Base

Acids and bases can be classified as either strong or weak based on their degree of dissociation (ionization) in water.

• A strong acid like hydrochloric acid ($\text{HCl}$) completely dissociates in water, releasing a large concentration of hydrogen ions ($\text{H}^+$).
• A strong base like sodium hydroxide ($\text{NaOH}$) completely dissociates in water, releasing a large concentration of hydroxide ions ($\text{OH}^-$).

Since $\text{NaCl}$ is formed from hydrochloric acid ($\text{HCl}$), which is a strong acid, and sodium hydroxide ($\text{NaOH}$), which is a strong base, common salt is made up of a strong acid and a strong base.

Analyzing the Options

Let's consider the given options in light of our understanding:

• Option 1: a strong acid and a weak base
  Example: Ammonium chloride ($\text{NH}_4\text{Cl}$) is formed from hydrochloric acid ($\text{HCl}$, a strong acid) and ammonium hydroxide ($\text{NH}_4\text{OH}$, a weak base). This is not $\text{NaCl}$.
• Option 2: a weak acid and a weak base
  Example: Ammonium acetate ($\text{CH}_3\text{COONH}_4$) is formed from acetic acid ($\text{CH}_3\text{COOH}$, a weak acid) and ammonium hydroxide ($\text{NH}_4\text{OH}$, a weak base). This is not $\text{NaCl}$.
• Option 3: a weak acid and a strong base
  Example: Sodium acetate ($\text{CH}_3\text{COONa}$) is formed from acetic acid ($\text{CH}_3\text{COOH}$, a weak acid) and sodium hydroxide ($\text{NaOH}$, a strong base). This is not $\text{NaCl}$.
• Option 4: a strong acid and a strong base
  Example: Sodium chloride ($\text{NaCl}$) is formed from hydrochloric acid ($\text{HCl}$, a strong acid) and sodium hydroxide ($\text{NaOH}$, a strong base). This matches the composition of common salt.

Therefore, common salt ($\text{NaCl}$) is made up of a strong acid and a strong base.

Revision Table: Salt Formation Types

Additional Information on Salt Properties

The pH of a salt solution depends on the strength of the parent acid and base.

• Salts of strong acid and strong base result in neutral solutions (pH ≈ 7).
• Salts of strong acid and weak base result in acidic solutions (pH < 7).
• Salts of weak acid and strong base result in basic solutions (pH > 7).
• Salts of weak acid and weak base can be neutral, slightly acidic, or slightly basic, depending on the relative strengths of the acid and base.

Since $\text{NaCl}$ is formed from a strong acid and a strong base, an aqueous solution of $\text{NaCl}$ is neutral.